1. Field of the Invention
The present invention relates to a microscopic magneto-resistive effect element and a microscopic magneto-resistive effect memory cell, an MRAM including a plurality of such magneto-resistive effect elements or a plurality of magneto-resistive effect memory cells integrated at a high density, and a method for performing information write or read to or from the microscopic magneto-resistive effect memory cell.
2. Description of the Related Art
A magnetic random access memory (MRAM) using a magneto-resistive (MR) film was proposed by L. J. Schwee, Proc. INTERMAG Conf. IEEE Trans. on Magn. Kyoto (1972) pp. 405. Various types of MRAMs including word lines as current lines for generating a magnetic field and sense lines using MR films for reading data have been studied. One of such studies is described in A. V. Pohm et al., IEEE Trans. on Magn. 28 (1992) pp. 2356. Such memory devices generally use an NiFe film or the like exhibiting an anisotropic MR effect (AMR) having an MR change ratio of about 2%, and thus the level of an output signal needs to be improved.
M. N. Baibich et al., Phys. Rev. Lett. 61 (1988) pp. 2472 describes that an artificial lattice film formed of magnetic films exchange-coupled through a nonmagnetic film to each other shows a giant MR effect (GMR). K. T. M. Ranmuthu et al., IEEE Trans. on Magn. 29 (1993) pp. 2593 proposes an MRAM using a GM film formed of magnetic films antiferromagnetically exchanged-coupled to each other. The GMR film exhibits a relatively large MR change ratio, but disadvantageously requires a larger magnetic field to be applied and thus requires a larger current for writing and reading information than an AMR film.
One exemplary type of non-coupling GMR film is a spin valve film. B. Dieny et al., J. Magn. Magn. Mater. 93 (1991) pp. 101 describes a spin valve film using an antiferromagnetia film. H. Sakakima et al., Jpn. J. Appl. Phys. 33 (1994) pp. L1668 describes a spin valve film using a semi-hard magnetic film. These spin valve films require a magnetic field as small as that required by the AMR films and still exhibit a larger MR change ratio than the AMP films. Y. Irie et al., Jpn. J. Appl. Phys. 34 (1995) pp. L415 describes an MRAM, formed of a spin valve film using an antiferromagnetic film or a hard magnetic film, which performs a non-destructive read out (NDRO).
The nonmagnetic film used for the above-described GMR films is a conductive film formed of Cu or the like. Tunneling GMR films (TMR) using Al2O3, MgO or the like as the nonmagnetic film have actively been studied, and MRAMs using the TMR film have been proposed.
It is known that the MR effect provided when a current flows perpendicular to the surface of a GMR film (CPPMR) is larger than the MR effect provided when a current flows parallel to the surface of the GMR film (CIPMR). A TMR film, which has a relatively high impedance, is expected to provide a sufficiently large output.
However, reduction in the size of an MRAM generates the following problems. A magnetic film usually has a thickness of about 1 nm to about 10 nm. In an MRAM having a width of on the order of submicrometers, the strength of an anti-magnetic field component is not negligible, and thus a relatively large magnetic field is required to magnetize the magnetic film. A relatively large magnetic coercive force is also required to maintain the magnetized state of the magnetic film. Thus, it is difficult to invert the magnetization by a magnetic field which is generated by a current flowing in word lines.
According to one aspect of the invention, a magneto-resistive effect element includes a first ferromagnetia film; a second ferromagnetic film; and a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film has an effective magnetic thickness of about 2 nm or less.
In one embodiment of the invention, at least one of the first ferromagnetic film and the second ferromagnetic ad film has a magnetization direction in a planar direction thereof.
In one embodiment of the invention, the second ferromagnetic film is formed of XMnsb, where X is at least one element selected from the group consisting of Ni, Pt, Pd and Cu.
In one embodiment of the invention, the first ferromagnetic film includes an amorphous magnetic film, and a third ferromagnetic film in contact with the first nonmagnetic film and interposed between the amorphous magnetic film and the first nonmagnetic film.
In one embodiment of the invention, the third ferromagnetic film has a thickness of about 0.2 nm or more and about 2 nm or less.
In one embodiment of the invention, the third ferromagnetic film has a thickness of about 0.8 nm or more and about 1.2 nm or less.
In one embodiment of the invention, the amorphous magnetic film includes at least one selected from the group consisting of CoFeB and CoMnB.
In one embodiment of the invention, the first ferromagnetic film includes a second nonmagnetic film, a fourth ferromagnetic film, and a fifth ferromagnetic film. The fourth ferromagnetic film and the fifth ferromagnetic film are antiferromagnetically exchange-coupled with each other through the second nonmagnetic film.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have different strengths of saturated magnetization from each other.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have different thicknesses from each other.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have a thickness difference of about 2 nm or less.
In one embodiment of the invention, the second nonmagnetic film is formed of Ru.
In one embodiment of the invention, the second nonmagnetic film is formed of one of Rh, Ir and Re.
In one embodiment of the invention, the second nonmagnetic film has a thickness of about 0.6 nm or more and about 0.8 nm or less.
In one embodiment of the invention, at least one of the fourth ferromagnetic film and the fifth ferromagnetic film contains at least one element selected from the group consisting of Ni, Co and Fe as a main component.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film are magnetization-rotated while being kept anti-parallel to each other.
In one embodiment of the invention, the second ferromagnetic film includes a third nonmagnetic film, a sixth ferromagnetic film, and a seventh ferromagnetic film. The sixth ferromagnetic film and the seventh ferromagnetic film are antiferromagnetically exchange-coupled with each other through the third nonmagnetic film.
In one embodiment of the invention. the third nonmagnetic film it formed of Ru.
In one embodiment of the invention, the third nonmagnetic film is formed of one of Rh, Ir and Re.
In one embodiment of the invention, the third nonmagnetic film has a thickness of about 0.6 nm or more and about 0.8 nm or less.
In one embodiment of the invention, at least one of the sixth ferromagnetic film and the seventh ferromagnetic film contains at least one element selected from the group consisting of Ni, Co and Fe as a main component.
In one embodiment of the invention, the first nonmagnetic film is an insulating film.
In one embodiment of the invention, the insulating film contains at least one selected from the group consisting of Al2O3, MgO, a carbide and a nitride.
According to another aspect of the invention, a magneto-resistive effect memory cell includes a first ferromagnetic film; a second ferromagnetic film; a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film; and at least one conductive film for causing a magnetization rotation of at least the first ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film has an effective magnetic thickness of about 2 nm or less.
In one embodiment of the invention, at least one of the first ferromagnetic film and the second ferromagnetic film has a magnetization direction in a planar direction thereof.
In one embodiment of the invention, the second ferromagnetic film is formed of XMnSb, where X is at least one element selected from the group consisting of Ni, Pt, Pd and Cu.
In one embodiment of the invention, the first ferromagnetic film includes an amorphous magnetic film, and a third ferromagnetic film in contact with the first nonmagnetic film and interposed between the amorphous magnetic film and the first nonmagnetic film.
In one embodiment of the invention, the third ferromagnetic film has a thickness of about 0.2 nm or more and about 2 nm or less.
In one embodiment of the invention, the third ferromagnetic film has a thickness of about 0.8 nm or more and about 1.2 nm or less.
In one embodiment of the invention, the amorphous magnetic film includes at least one selected from the group consisting of CoFeB and CoMnB.
In one embodiment of the invention, the first ferromagnetic film includes a second nonmagnetic film, a fourth ferromagnetic film, and a fifth ferromagnetic film. The fourth ferromagnetic film and the fifth ferromagnetic film are antiferromagnetically exchange-coupled with each other through the second nonmagnetic film.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have different strengths of saturated magnetization from each other.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have different thicknesses from each other.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have a thickness difference of about 2 nm or less.
In one embodiment of the invention, the second nonmagnetic film is formed of Ru.
In one embodiment of the invention, the second nonmagnetic film is formed of one of Rh, Ir and Re.
In one embodiment of the invention, the second nonmagnetic film has a thickness of about 0.6 nm or more and about 0.8 nm or less.
In one embodiment of the invention, at least one of the fourth ferromagnetic film and the fifth ferromagnetic film contains at least one element selected from the group consisting of Ni, Co and Fe as a main component.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film are magnetization-rotated while being kept anti-parallel to each other.
In one embodiment of the invention, the second ferromagnetic film includes a third nonmagnetic film, a sixth ferromagnetic film, and a seventh ferromagnetic film. The sixth ferromagnetic film and the seventh ferromagnetic film are antiferromagnetically exchange-coupled with each other through the third nonmagnetic film.
In one embodiment of the invention, the third nonmagnetic film is formed of Ru.
In one embodiment of the invention, the third nonmagnetic film Is formed of one of Rh, Ir and Re.
In one embodiment of the invention, the third nonmagnetic film has a thickness of about 0.6 nm or more and about 0.8 nm or less.
In one embodiment of the invention, at least one of the sixth ferromagnetic film and the seventh ferromagnetic film contains at least one element selected from the group consisting of Ni, Co and Fe as a main component.
In one embodiment of the invention, the first nonmagnetic film is an insulating film.
In one embodiment of the invention, the insulating film contains at least one selected from the group consisting of Al2O3, MgO, a carbide and a nitride.
In one embodiment of the invention. at least two layer structures are provided, each layer structure including the first ferromagnetic film, the second ferromagnetic film, and the first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The at least two layer structures are stacked with at least one fourth nonmagnetic film interposed therebetween.
In one embodiment of the invention, the second ferromagnetic films of the at least two layer structures have different magnetic coercive forces from each other.
According to still another aspect of the invention, an MRAM Includes a plurality of the above-described magneto-resistive effect memory cells. The plurality of conductive films are arranged in at least one prescribed direction.
According to still another aspect of the invention, a magneto-resistive effect element includes a first ferromagnetic film; a second ferromagnetic film; and a nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film includes an amorphous magnetic film, and a third ferromagnetic film in contact with the nonmagnetic film and interposed between the amorphous magnetic film and the nonmagnetic film.
In one embodiment of the invention, at least one of the first ferromagnetic film and the second ferromagnetic film has a magnetization direction in a planar direction thereof.
In one embodiment of the invention, the nonmagnetic film is an insulating film.
According to still another aspect of the invention, a magneto-resistive effect element includes a first ferromagnetic film; a second ferromagnetic film; and a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film includes a second nonmagnetic film, a third ferromagnetic film, and a fourth ferromagnetic film. The third ferromagnetic film and the fourth ferromagnetic film are antiferromagnetically exchange-coupled with each other through the second nonmagnetic film.
In one embodiment of the invention, at least one of the first ferromagnetic film and the second ferromagnetic film has a magnetization direction in a planar direction thereof.
In one embodiment of the invention, the third ferromagnetic film and the fourth ferromagnetic film have different strengths of saturated magnetization from each other.
In one embodiment of the invention, the third ferromagnetic film and the fourth ferromagnetic film have different thicknesses from each other.
In one embodiment of the invention, the third ferromagnetic film and the fourth ferromagnetic film are magnetization-rotated while being kept anti-parallel to each other.
In one embodiment of the invention, the second ferromagnetic film includes a third nonmagnetic film, a fifth ferromagnetic film, and a sixth ferromagnetic film. The fifth ferromagnetic film and the sixth ferromagnetic film are antiferromagnetically exchange-coupled with each other through the third nonmagnetic film.
In one embodiment of the invention, the first nonmagnetic film is an insulating film.
According to still another aspect of the invention, a magneto-resistive effect memory cell includes a first ferromagnetic film; a second ferromagnetic film; a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film; and at least one conductive film for causing a magnetization rotation of at least the first ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable the a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film includes an amorphous magnetic film, and a third nonmagnetic film in contact with the first nonmagnetic film and interposed between the amorphous film and the first nonmagnetic film.
In one embodiment of the invention, at least one of the first ferromagnetic film and the second ferromagnetic film has a magnetization direction in a planar direction thereof.
In one embodiment of the invention, the first nonmagnetic film is an insulating film.
In one embodiment of the invention, at least two layer structures are provided, each layer structure including the first ferromagnetic film, the second ferromagnetic film, and the first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The at least two layer structures are stacked with at least one second nonmagnetic film interposed therebetween.
In one embodiment of the invention, the second ferromagnetic films of the at least two layer structures have different magnetic coercive forces from each other.
According to still another aspect of the invention, an MRAM includes a plurality of the above-described magneto-resistive effect memory cells. The plurality of conductive films are arranged in at least one prescribed direction.
According to still another aspect of the invention, a magneto-resistive effect memory cell includes a first ferromagnetic film; a second ferromagnetic film; a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film; and at least one conductive film for causing a magnetization rotation of at least the first ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film includes a second nonmagnetic film, a third ferromagnetic film, and a fourth ferromagnetic film. The third ferromagnetic film and the fourth ferromagnetic film are antiferromagnetically exchange-coupled with each other through the second nonmagnetic film.
In one embodiment of the invention, a magneto-resistive effect memory cell at least one of the first ferromagnetic film and the second ferromagnetic film has a magnetization direction in a planar direction thereof.
In one embodiment of the invention, the third ferromagnetic film and the fourth ferromagnetic film have different strengths of saturated magnetization from each other.
In one embodiment of the invention, the third ferromagnetic film and the fourth ferromagnetic film have different thicknesses from each other.
In one embodiment of the invention, the third ferromagnetic film and the fourth ferromagnetic film are magnetization-rotated while being kept anti-parallel to each other.
In one embodiment of the invention, the second ferromagnetic film includes a third nonmagnetic film, a fifth ferromagnetic film, and a sixth ferromagnetic film.
The fifth ferromagnetic film and the sixth ferromagnetic film are antiferromagnetically exchange-coupled with each other through the third nonmagnetic film.
In one embodiment of the invention, the first nonmagnetic film is an insulating film.
In one embodiment of the invention, at least two layer structures are provided, each layer structure including the first ferromagnetic film, the second ferromagnetic film, and the first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The at least two layer structures are stacked with at least one fourth nonmagnetic film interposed therebetween.
In one embodiment of the invention, the second ferromagnetic films of the at least two layer structures have different magnetic coercive forces from each other.
According to still another aspect of the invention, an MRAM includes a plurality of the above-described magneto-resistive effect memory cells. The plurality of conductive films are arranged in at least one prescribed direction.
According to still another aspect of the invention, a method for writing information to and reading information from a magneto-resistive effect memory cell is provided. The magneto-resistive effect memory cell includes a first ferromagnetic film, a second ferromagnetic film, a nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film, and at least one conductive film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The method includes the steps of causing a first current to flow in the at least one conductive film to cause a magnetization rotation of at least the first ferromagnetic film, thereby writing information in the magneto-resistive effect memory cell; and causing a second current to flow in the first ferromagnetic film, the nonmagnetic film, and the second ferromagnetic film, and causing a third current, which is a combination of a positive bias current and a negative bias current, to flow in the at least one conductive film, thereby reading a voltage value corresponding to the second current and thus reading information written in the magneto-resistive element memory cell.
In one embodiment of the invention, the third current has a level which causes a magnetization rotation of the first ferromagnetic film but does not cause a magnetization rotation of the second ferromagnetic film.
According to still anther aspect of the invention, a method for writing information to and reading information from an MRAM including a plurality of magneto-resistive effect memory cells is provided. Each magneto-resistive effect memory cell includes a first ferromagnetic film, a second ferromagnetic film, a nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film, and at least one conductive film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The plurality of conductive films are arranged in at least one prescribed direction. The method includes the steps of causing a first current to flow in the at least one conductive film of a first magneto-resistive effect memory cell of the plurality of magneto-resistive effect memory cells to cause a magnetization rotation of at least the first ferromagnetic film of the first magneto-resistive effect memory cell, thereby writing information in the first magneto-resistive effect memory cell; and causing a second current to flow in the first ferromagnetic film, the nonmagnetic film, and the second ferromagnetic film of the first magneto-resistive effect memory cell, and causing a third current, which is a combination of a positive bias current and a negative bias current, to flow in the at least one conductive film of the first magneto-resistive effect memory cell, thereby reading a voltage value corresponding to the second current and thus reading information written in the first magneto-resistive effect memory cell.
In one embodiment of the invention, the third current has a level which causes a magnetization rotation of the first ferromagnetic film but does not cause a magnetization rotation of the second ferromagnetic film.
In one embodiment of the invention, the method further includes the step of causing a fourth current to flow in the at least one conductive film of a second magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell. the fourth current flowing in a direction for canceling a magnetic field leaked to a third magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell.
In one embodiment of the invention, the second magneto-resistive effect memory cell is identical with the third magneto-resistive effect memory cell.
According to still another aspect of the invention, a method for reading information from a magneto-resistive effect memory cell is provided. The magneto-resistive effect memory cell includes a first ferromagnetic film, a second ferromagnetic film, a nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film, and at least one conductive film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The method includes the step of causing a first current to flow in the first ferromagnetic film, the nonmagnetic film, and the second ferromagnetic film, and causing a second current, which is a combination of a positive bias current and a negative bias current, to flow in the at least one conductive film, thereby reading a voltage value corresponding to the first current and thus reading information written in the magneto-resistive effect memory cell.
In one embodiment of the invention, the second current has a level which causes a magnetization rotation of the first ferromagnetic film but does not cause a magnetization rotation of the second ferromagnetic film.
According to still another aspect of the invention, a method for reading information from an MRAM including a plurality of magneto-resistive effect memory cells is provided. Each magneto-resistive effect memory cell includes a first ferromagnetic film, a second ferromagnetic film, a nonmagnetic film interposed between the first ferromagnetic, film and the second ferromagnetic film, and at least one conductive film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The plurality of conductive films are arranged in at least one prescribed direction. The method includes the step of causing a first current to flow in the first ferromagnetic film, the nonmagnetic film, and the second ferromagnetic film of a first magneto-resistive effect memory cell of the plurality of magneto-resistive effect memory cells, and causing a second current, which is a combination of a positive bias current and a negative bias current, to flow in the at least one conductive film of the first magneto-resistive effect memory cell, thereby reading a voltage value corresponding to the first current and thus reading information written in the first magneto-resistive effect memory cell.
In one embodiment of the invention, the second current has a level which causes a magnetization rotation of the first ferromagnetic film but does not cause a magnetization rotation of the second ferromagnetic film.
In one embodiment of the invention, the method further includes the step of causing a third current to flow in the at least one conductive film of a second magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell, the third current flowing in a direction for canceling a magnetic field leaked to a third magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell.
In one embodiment of the invention, the second magneto-resistive effect memory cell is identical with the third magneto-resistive effect memory cell.
According to still another aspect of the invention, a method for writing multiple levels of a signal to and reading multiple levels of a signal from a magneto-resistive effect memory cell is provided. The magneto-resistive effect memory cell includes at least two layer structures; at least one first nonmagnetic film interposed between the at least two layer structures; and at least one conductive film. Each of the at least two layer structures includes a first ferromagnetic film, a second ferromagnetic film, and a second nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film. The method includes the steps of causing a first current in the at least one conductive film to cause a magnetization rotation of at least one of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures, or to cause a magnetization rotation of none of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures, thereby writing multiple levels of a signal in the magneto-resistive affect memory cell; and causing a second current to each of the at least two layer structures to compare a resistance value corresponding to the second current and a reference resistance value, thereby reading the multiple levels. of the signal written in the magneto-resistive effect memory cell.
In one embodiment of the invention, the method further includes the step of causing a current which rises in a gradually increasing manner to flow in the at least one conductive film.
According to still another aspect of the invention, a method for writing multiple levels of a signal to a magneto-resistive effect memory cell is provided. The magneto-resistive effect memory cell includes at least two layer structures; at least one first nonmagnetic film interposed between the at least two layer structures; and at least one conductive film. Each of the at least two layer structures includes a first ferromagnetic film, a second ferromagnetic film, and a second nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film. The method includes the steps of causing a first current to flow in the at least one conductive film to cause a magnetization rotation of at least one of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures, or to cause a magnetization rotation of none of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures, thereby writing multiple levels of a signal In the magneto-resistive effect memory cell.
According to still another aspect of the invention, a method for reading multiple levels of a signal from a magneto-resistive effect memory cell is provided. The magneto-resistive effect memory cell includes at least two layer structures; at least one first nonmagnetic film interposed between the at least two layer structures; and at least one conductive film. Each of the at least two layer structures includes a first ferromagnetic film, a second ferromagnetic film, and a second nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film. The method includes the steps of causing a first current to flow in each of the at least two layer structures to compare a resistance value corresponding to the first current and a reference resistance value, thereby reading multiple levels of a signal written in the magneto-resistive effect memory cell.
In one embodiment of the invention, the method further includes the step of causing a current which rises in a gradually increasing manner to flow in the at least one conductive film.
According to still another aspect of the invention, a method for writing multiple levels of a signal to and reading multiple levels of a signal from an MRAM including a plurality of magneto-resistive effect memory cells is provided. Each magneto-resistive effect memory cell includes at least two layer structures; at least one first nonmagnetic film interposed between the at least two layer structures: and at least one conductive film. Each of the at least two layer structures includes a first ferromagnetic film, a second ferromagnetic film, and a second nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film The plurality of conductive films are arranged in at least one prescribed direction. The method includes the steps of causing a first current to flow in the at least one conductive film of a first magneto-resistive effect memory cell of the plurality of magneto-resistive effect memory cells to cause a magnetization rotation of at least one of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures of the first magneto-resistive effect memory cell, or to cause a magnetization rotation of none of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures of the first magneto-resistive effect memory cell, thereby writing multiple levels of a signal in the first magneto-resistive effect memory cell; and causing a second current to flow in each of the at least two layer structures of the first magneto-resistive effect memory cell to compare a resistance value corresponding to the second current and a reference resistance value, thereby reading the multiple levels of the signal written in the first magneto-resistive effect memory cell.
In one embodiment of the invention, the method further includes the step of causing a current which rises in a gradually increasing manner to flow in the at least one conductive film.
In one embodiment of the invention, the method further includes the step of causing a third current to flow in the at least one conductive film of a second magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell, the third current flowing in a direction for canceling a magnetic field leaked to a third magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell.
In one embodiment of the invention, the second magneto-resistive effect memory cell is identical with the third magneto-resistive effect memory cell.
According to still another aspect of the invention, a method for writing multiple levels of a signal in an MRAM including a plurality of magneto-resistive effect memory cells is provided. Each magneto-resistive effect memory cell includes at least two layer structures; at least one first nonmagnetic film interposed between the at least two layer structures; and at least one conductive film. Each of the at least two layer structures includes a first ferromagnetic film, a second ferromagnetic film, and a second nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film. The plurality of conductive films are arranged in at least one prescribed direction. The method includes the steps of causing a first current of flow in the at least one conductive film of a first magneto-resistive effect memory cell of the plurality of magneto-resistive effect memory cells to cause a magnetization rotation of at least one of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures of the first magneto-resistive effect memory cell, or to cause a magnetization rotation of none of the first ferromagnetic film and the second ferromagnetic film of each of the at least two layer structures of the first magneto-resistive effect memory cell, thereby writing multiple levels of a signal in the first magneto-resistive effect memory cell.
In one embodiment of the invention, the method further includes the step of causing a second current to flow in the at least one conductive film of a second magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell, the second current flowing in a direction for canceling a magnetic field leaked to a third magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell
In one embodiment of the invention, the second magneto-resistive effect memory cell is identical with the third magneto-resistive effect memory cell.
According to still another aspect of the invention, a method for reading multiple levels of a signal from an MRAM including a plurality of magneto-resistive effect memory cells is provided. Each magneto-resistive effect memory cell includes at least two layer structures; at least one first nonmagnetic film interposed between the at least two layer structures; and at least one conductive film. Each of the at least two layer structures includes a first ferromagnetic film, a second ferromagnetic film, and a second nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film. The plurality of conductive films are arranged in at least one prescribed direction. The method includes the steps of causing a first current to flow in each of the at least two layer structures of a first magneto-resistive effect memory cell of the plurality of magneto-resistive effect memory cells to compare a resistance value corresponding to e the first current and a reference resistance value, thereby reading multiple levels of a signal written in the first magneto-resistive effect memory cell.
In one embodiment of the invention, the method further includes the step of causing a current which rises in a gradually increasing manner to flow in the at least one conductive film.
In one embodiment of the invention, the method further includes the step of causing a second current to flow in the at least one conductive film of a second magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell, the second current flowing in a direction for canceling a magnetic field leaked to a third magneto-resistive effect memory cell other than the first magneto-resistive effect memory cell.
In one embodiment of the invention, the second magneto-resistive effect memory cell is identical with the third magneto-resistive effect memory cell.
According to one aspect of the present invention, a free layer in which the magnetization direction is relatively easily rotatable by the external magnetic field includes a ferromagnetic film having a small magnetic coercive force even though being thin, and an amorphous film. According to another aspect of the present invention, a free layer includes a synthesized ferromagnetic film including ferromagnetic films which are antiferromagnetically exchange-coupled to each other.
Thus, the invention described herein makes possible the advantages of providing a microscopic magnetic magneto-resistive effect element and a microscopic magneto-resistive effect memory cell which include a ferromagnetic film and are sufficiently easily operable as a result of the strength of the anti-magnetic component of the ferromagnetic film being reduced, an MRAM including a plurality of such magneto-resistive effect elements or a plurality of magneto-resistive effect memory cells integrated at a high density, and a method for performing information write or read to or from the microscopic magneto-resistive effect memory cell.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.